BACKGROUND: Uncontrolled hypertension, a major concern among hypertensive patients, may be caused by various factors such as inadequate knowledge and inappropriate attitude, unhealthy lifestyle, and ineffective treatment. The present study tried to cast light on factors leading to uncontrolled hypertension. METHODS: In this cross-sectional study, all hypertensive participants of the third phase of the Isfahan Healthy Heart Program were contacted and invited to take part in the study. A questionnaire including knowledge of and attitude toward hypertension and its control and treatment methods, and practice about lifestyle and pharmacological treatment was completed for all patients who consented to participate. The participants’ anthropometric indices and blood pressure were then measured. Chi-square and Student’s t-tests were used to compare the groups with controlled and uncontrolled blood pressure. The effect of each factor on uncontrolled blood pressure was assessed by employing stepwise logistic regression. RESULTS: Of 114 participants, 43 (37.12%) and 71 (62.28%) individuals had controlled and uncontrolled blood pressure, respectively. Stepwise logistic regression revealed body mass index > 25 kg/m2 to have the greatest effects on uncontrolled blood pressure [Odds ratio (OR) = 13.091, Confidence interval of 95% (95% CI): 1.437-116.352, P = 0.021). In addition, male gender increased the risk for uncontrolled blood pressure (OR = 8.475, CI95%: 1.276-56.313, P = 0.027), while inappropriate attitude decreased the mentioned risk (OR = 0.047, CI95%: 0.007-0.318, P = 0.002). CONCLUSION: According to our findings, obesity is the most important cause of uncontrolled blood pressure. Therefore, weight has to be closely monitored and controlled in hypertensive patients.